time conversions

dear friends - sorry to ask another simple question -
I have dates set up as this:
dates  #[1] 2003-01-21 01:08:00

To handle it I did
as.POSIXlt(dates)  "2003-01-21 01:08:00 CET"

but noticed that during write.table it was apparently better to take it 
further
as.numeric(as.POSIXct(as.POSIXlt(dates))   1043107680

And this works fine for modeling but now I would like to have it back as 
POSIXlt
as.POSIXlt requires an origin, if I'm right.
So how is it done?

Best wishes

Troels Ring
Aalborg
Denmark